1. Field of the Invention
This invention relates generally to elevator security systems employing a voice-recognition device to control access to the elevator car, and more particularly to such a voice-recognition device that can be effective even when the user is suffering a throat affliction that changes the user's vocal characteristics.
2. Description of the Prior Art
Although the chief responsibility of the elevator attendant in older elevator systems was to operate the elevator car, the elevator attendant also provided a degree of security by limiting access to authorized, or at least familiar, passengers. With the advent of the user-operated elevator system, and the demise of the elevator attendant, it has become necessary to provide an elevator security system to insure that only authorized personnel have access to the elevator car. Access control is critical in high-rise office buildings and especially in living units where the elevator system must operate twenty-four hours a day. It is impossible for building security personnel to effectively monitor elevator use and prohibit unauthorized users from gaining access to an elevator car with today's widespread use of multi-car elevator systems. Obviously, the problem of unauthorized use is especially critical in landings above the main landing where security personnel are not routinely stationed.
For comprehensive protection, an elevator security system must control use of the elevator car in two different situations. First, the security system must detect a hall call initiated by an unauthorized user at any landing. The elevator system should not respond to such calls thereby preventing the unauthorized user from gaining access to an elevator car. Second, once an authorized user has entered an elevator car and initiated a car call to the desired landing, by actuating the proper switch, the security system must insure that the authorized user is permitted access to the landing selected. If the authorized user is prohibited access to the selected landing the car call should be disregarded. Furthermore, the security system should be designed such that unauthorized users do not gain access to an elevator car or landing by simply observing an authorized user entering a code or by obtaining the code through other deceptive means.
One prior art elevator security system is disclosed in a commonly assigned U.S. Pat. No. 4,534,056 entitled "Voice Recognition Elevator Security System" (Ser. No. 411,792 filed Aug. 26, 1982). The application discloses a system that controls access to an elevator system by analyzing the user's voice signal and comparing the results with the voice signals of all authorized users stored in memory. One expected problem with such a recognition system is the failure to recognize an authorized user due to changes in the authorized user's vocal characteristics. This problem is overcome by the present invention whereby the stored signals can be temporarily modified when the user is suffering from laryngeal indisposition (i.e. sore throat), that causes changes in the user's voice patterns. These and other advantages of the present invention are discussed below in the description of the preferred embodiments.